The Ceratodon purpureus Transcriptome

The genome sequence of the model moss, Physcomitrella patens, has significantly enhanced our understanding on the evolution of developmental processes in land plants. However, the bryophytes themselves are a morphologically and ecologically diverse group of plants and thus development of genomic resources for a diverse array of species is highly needed. To facilitate molecular analyses of bryophyte diversity, we have developed genomic resources for another moss model system, Ceratodon pupureus, recently adopted for genome sequencing. C. purpureus last shared a common ancestor with P. patens approximately 200 MYA from which it differs in its mating system. P. patens is hermaphroditic, while C. purpureus has separate, chromosomally-determined sexes with separate male and female haploid plants. These contrasting life histories are expected to drive major differences in genome architecture.

As the first step toward this goal, we describe 454-FLX pyrosequencing of protonemal transcriptomes from a male and female genotype of C. purpureus, and discuss this resource in the context of the evolution of land plant genomes, the evolution of sexual dimorphism, and the responses to dehydration stress. We find (i) many of the same genes as in Physcomitrella; (ii) extensive expression and genetic divergence between the male and female genotypes; (iii) highly conserved codon usage bias across P. patens and C. purpureus; (iv) evidence of an ancient gene duplication; (v) using ABA-responses as an example, that mining the sequence resource can be effectively used to identify hormone- and stress-induced genes.